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Hi, I'm Paul from the East of the UK. I decided to join this forum after watching some of the excellent GS videos about powerjack inverters and the wealth of useful information on this forum.
I started off my experimentation with off-grid solar about 4 years ago when a friend sold me very cheaply a 'classic' powerjack inverter (v3 boards dated 2013) rated at 8000 chinese watts and four 180Ah truck batteries (which were past their best). I bought all the other stuff myself such as six 60-cell solar panels, an EPever Tracer 4210AN charge controller, and started playing seeing what I could run off grid.
In the end I had 4 solar panels mounted on the garage roof and another 4 mounted on metal framework in the garden, all SE facing with minimal shading except in winter months, in a 2S4P configuration, obviously with all the necessary fuses, diodes etc between the strings and a suitable rated DC isolator.
I now have six 200Ah Rosen Solar gel SLA batteries in a 2S3P configuration, each string fused with 100A HRC fuses, an EPever Triron 4210AN controller with a cat5 cable back to a wifi module in the house, and the 'load' output of the inverter drives a relay to switch the inverter on/off remotely. The output of the inverter is protected by a 16A RCBO.
Inside the house, I have rewired one ring main and the lighting circuit to a 40A 2PCO changeover switch with centre-off to enable me to switch those circuits fsafely rom the main grid CU to the inverter at will.
This has worked well, and can provide 3.6kW before the PJ starts complaining. Thankfully in the UK as everything is 240V I don't have any of the issues that the US/AU guys have with 'split phase' 110v, which has always seemed an illogical complication to me. having a simple, single 220-240v output seems far more sensible to my little brain!
Knowing that the PJ inverter was old and potentially unreliable (as well as having a high idle current of 2.5A @24V) I decided to try buying a new 'Upower' badged 8k inverter in Dec 2020. This arrived from China in good condition and working order, however I noticed that it only had an ASL3 transformer, and that LED lights would dim noticeably more than they did with the ancient PJ inverter when heavy loads were applied (e.g. 2000W induction hob) and after some inspection with a newly bought scope saw the waveform severely cropped with any load above about 1.5kW. This made sense to me as the new upower unit was much lighter than the old PJ unit which contained two (AS2 if memory serves) transformers in series. Therefore I concluded that the electronics were well up the job, but the weak link was the transformer.
I decided to calculate and wind a transformer myself that wouldgive a properly formed sine wave and cope with a continuous 3.6kW+ for 20 mins at least. I found an ebay seller selling some big toroidal transformers that were originally designed for an audio amplifier application very cheaply. So I bought one. The core was 52cm2 CSA, which according to the calculations is good for up to 4VA. SO I stripped it down, and rewound it with 214 turns of 2mm dia (~3mm CSA) enamelled wire as the secondary, and 12 turns of 2*16mm2 PVC coated cable as the primary, each layer separated with fibreglass tape.
This transformer works extremely well, giving a clean sine wave up to 3kW or more. However the idle current is again a stubborn 2.5A like the older PJ. So now I am working on making a suitable choke to put in series with the transformer to lower the idle current.
However the idle current is again a stubborn 2.5A like the older PJ. So now I am working on making a suitable choke to put in series with the transformer to lower the idle current.
The easiest and quickest solution to reducing that no-load current? Force a second turn of wire around the stock PJ choke (assuming it has one!)
Works wonders; you should be able to get the no-load current down to around 1A...providing there aren't a half dozen filter caps on the "output" board.
Unless you're trying to run really high (relative) battery voltages (i.e. 32v into a 24v inverter), there is no discernible advantage to adding more chokes to the transformer primary.
and after some inspection with a newly bought scope saw the waveform severely cropped with any load above about 1.5kW.
If you're referring to the AC wave "flat-topping" (i.e. becoming progressively square as the load increases)...you're seeing the result of an improperly specced transformer voltage ratio. PJ seems to like using 18v -> 230v trannies for 24v inverters. Mathematically, 18v * sqrt(2) [1.414] = 25.452vDC absolute minimum battery for a pure sine wave output--at no load. If the load increases, due to transformer losses, this minimum voltage will also rise.
If there is insufficient headroom, the code will start to "flat-top" the waveform in an attempt to maintain voltage. (And of course the transformer gets louder as it's not getting a pure sine input.)
On GS inverters, we're between 15-16v for a 24v inverter (requiring 21.2 - 22.6v minimum).
Thankfully in the UK as everything is 240V I don't have any of the issues that the US/AU guys have with 'split phase' 110v, which has always seemed an illogical complication to me. having a simple, single 220-240v output seems far more sensible to my little brain!
Well, having grown up with "split phase", it does make sense...a little. 120v for everything except the powerhog appliances...but yes, the 2 voltages do provide a significant engineering challenge for an inverter ;-).
Thanks Sid for the warm welcome and the useful information for which you and Sean are well known! Given the knowledge and experience that I have obtained now, I would have bought a GS inverter in the first place. Nevertheless playing with PJ/Upower stuff with all it's quirks has helped me learn a lot.
The old 2013 PJ 8K is great; even with the resistor ladder altered to make it output ~245V RMS (which is comparable to the average grid voltage where I live) it produces a clean sine wave up to about 3.5kW which is when the overload LED comes on. This doesn't bother me as I know it is cheap chinese kit and never expected it to achieve the claimed figures. It's only downside is a high idle current of about 2.5A.
The 2020 Upower one which I got has a small ferrite with a single turn, which seems to keep the idle current down to 0.9A, but at anything above 1kW the sinewave peaks flatten and the peak to peak voltage reduces dramatically, to the point that it is almost a square wave above 3.5kW. Like you say, this is a combination of an incorrect winding ratio and a saturated core (too small). After building my own transformer and testing it with these boards (PJ rev 10.3C) I found that my new transformer does not fit either case, so decided to rebuild the Upower inverter as-is and take it with us to my wife's truly off-grid home in rural east africa if and when the farsical covid travel restrictions ease, as we will never need more than 2kW sustained there.
To that end I sourced a suitablly large and well ventilated casing (ex server), then deliberated as to what boards to use to build my new inverter. On some other forums people have used various boards from AliExpress, but comparing them to the PJ boards, the PJ boards are much larger, have more FETS, bigger caps and bigger heatsinks. So I decided to purchase a set of v11.1 PJ boards. Had I known at that time that GS could supply improved versions of the PJ boards with more configurability I would have done that, but sadly too late now. Nevertheless despite their imperfections, PJ boards with suitable external thermal control seem robust in my experience over the last 4 years. I would never trust PJ's own fan control system though!
Hopefully I will complete the build over the next few weeks and report back. I have a selection of chokes to test and probably re-wind, as I found the little PJ ferrite toroid to be ineffectual with my big transformer. Photos will follow in due course!
Nevertheless playing with PJ/Upower stuff with all it's quirks has helped me learn a lot.
Ha, it's where both Sean and I started 😉
Had I known at that time that GS could supply improved versions of the PJ boards with more configurability I would have done that, but sadly too late now.
Updated firmware for PJ boards perhaps...but the GS control boards are a COMPLETELY separate design, designed completely from the ground up at my desk.
We currently don't ship out of the country, simply due to the greatly increased difficulty of handling any service requirements...not to mention the much higher chance of getting scammed blind. But this may change at some point...
I have a selection of chokes to test and probably re-wind, as I found the little PJ ferrite toroid to be ineffectual with my big transformer.
Try 2 full turns around the PJ ferrite. I personally experimented with an E-core ferrite, but it was no better than the PJ ferrite. Had another customer glue 4 PJ ferrites together...and no load was not improved over a single PJ ferrite with 2 full turns.
The GS 12kw inverter uses 2 PJ ferrites, one on each leg of the transformer, 2 full turns each. (Probably would work the same with just one.) No load current @ 55v is under 0.75A...for a transformer that weighs mighty close to 100lbs, measuring just over 10x5 inches in size.
Welcome Paul.
This has worked well, and can provide 3.6kW before the PJ starts complaining. Thankfully in the UK as everything is 240V I don't have any of the issues that the US/AU guys have with 'split phase' 110v, which has always seemed an illogical complication to me. having a simple, single 220-240v output seems far more sensible to my little brain!
So how are UK construction sites doing the 110 Volts then? Just a step down transformer?
Yes just a 240-110v isolatiing transformer. The isolation is supposed to be fore safety, i.e. no referenced to ground so less risk of fatal shock when using equipment in wet weather outdoors.
I thought it was reffed to ground on the 110VAC side, but at +/- 55V with a centre tap pegged to ground for fault handling. 55VAC nominal will give you a wake up call if you manage to put yourself across it but won't kill you. Bear in mind that this is only what I've heard via youtubers such as John Ward. AFAIK nothing like that exists in Australia.